Machine key, expansion type



Jan. 9, 1968 R. R. DowNlE 3,362,734

Jan. 9, 1968 R. R. DowNlE 3,362,734

MACHINE KEY Filed July 11, 1983 I 3 Shets-Sheet 2 INVENTOR.

Jan. 9, 1968 R. R. DowNlE MACHINE KEY, ExPANsIoN TYPE 3 Sheets-Sheet 3 Filed July ll 1963 INVENTOR United States Patent C) 3,3a2,734 MACHINE KEY, EXEPANSION TWE Robert Rex Downie, 3328 College Ave., Beaver Falls, Fa. 15010 Fne July 11, 1963, ser. No. 294,369 7 Clairns. (Cl. 287-5205) The invention relates to improvements in machine keys for holding machine elements against relative movement at mutually contacting surfaces.

Objects of the invention are to provide a two-piece machine key that normally requires no hand fitting at assembly; that has pre-stressed working faces to withstand reverse shock loading and to hold the hub member from casual axial displacement; that may be shimmed at its working faces; that may, with its keyways, lie entirely Within the mutual contact area of the keyed members; and that may be set up or released as to pressuring of the working faces, at either end of the key. Specific objects of several forms of the invention disclosed herein will appear as the description proceeds.

Deficiencies of the current standard rectangularsectional integral keys, square and flat, straight and tapered and, as to hub entry, the Woodruif type also, are, in Summary, that they are not and cannot be so made and installed as to have opposing pre-load of their working faces; that even for their un-stressed fit they require hand filing and/or selective assembly with their keyways; that they cannot be shimmed at their working faces; and that principally for the first reason above, they all develop motion, begin to looseu, that is begin slowly to fail, after the first two or three hard and sharp reverse cycles of operation. T'he key of the present inven`- tion remedes the cited difficulties of the standard keys in ways and degrees which will appear as the various forms and features are described and explained.

'In the accompanying drawings are shown three illustrative forms of the expansion key of this invention. Referring particularly to the drawings:

FIG. l is a side elevation of a generally hexagonal key embodying the invention, showing in section adjacent portions of the keyed hub and shaft, showing at one side the adjacent portion of another wheel bushed for free rotation, and showing at theother side a portion of a pillow block mounting an antifriction bearing.

FIG. 2 is a plan view of the key of FIG. 1 with the shaft keyway, showing the lip relief.

FIG. 3 is a cross section on line 3-3 of FIG. 1, showing one end of the key of FIG. 1.

FIG. 4 is an enlarged sectional view of the key of FIG. 1 taken on line 4-4 in FIG. 2, including certain adjacent portions of hub and shaft.

FIG. 5 is a partial reproduction of the key of FIG. 4 with a shim added at the right lower face, and with the involved modifications of key and keyways.

FIG. 6 is a perspective view of one part of the key of FIGS. 1-4.

FIG. 7 is a side elevation of a -key of rectangular section also embodying the invention.

FIG. 8 is a top plan view yof the key of FIG. 7.

FIG. 9 is an end elevation of the :key of FIG. 7.

FIG. 10 is a top plan view of a third form of -key having a generally square cross section.

FIG. ll is a side elevation of the key of FIG. 10.

FIG. 12 is an enlarged section taken on line 12-12 of FIG. 10, with adjacent portions of hub and shaft in section.

The present invention is an improvement on the invention disclosed in my co-pending application Serial No. 325,808 filed November 19, 1963, entitled Machine Keys, which is a continuation of my application Serial No. 709,635 filed January 17, 1958, but now abandoned.

Referring to the accompanying drawngs, it should first be explained that letters are used therein to denote mechanically separable parts of structure and numerals to indicate particular points, lines or surfaces; each reference character, when shown in more than one view, designating the same element; and all longitudinal slope angles being exaggerated for clarity.

In FIGS. 1 to 4 inclusive, A and B are the two halves of a machine key. C (FIGS. 1,3) is the keyed portion of a shaft and D the keyed portion of a wheel hub mounted upon the shaft C. E represents a second wheel, with bushing F, in running contact at 39 with the left end of keyed hub D. G is an axially fixed bearing in housing H carrying one end of the shaft assemblage. 1, 3 (PIG. 4) are the two upper pressure faces of the key, each having a shallow median relief area, 2, 4 respectively, of substantial and unform width and extending the full length of the face. 5, 6 are the two lower pressure faces engaging the shaft keyway. 26, 27 are respectively the hub and shaft keyway floors which have a substantial clearance from the top surfaces 7, 8 and bottom surfaces 9, 10 of the key halves. Narrow lateral faces 11, 12 of the key are the intervals between upper and lower pressure faces and are equal in depth to the relief cut at the sides of the shaft keyway. v13 is the common arc of the shaft surface and the hub bore, interrupted by the keyageg Circled points 14, 15 on arc 13 are spaced apart a distance proportional to the width of the key and determine the width and elevation of the relief Shoulders 20, 21 on the shaft. From these Shoulders the depth of the shaft keyway is gaged and from the gage points 14, 15 the depth of the hub keyway is measured. Circled points 16, 17 indicate the shaft keyway lip lines and 18, 19 the hub keyway lip lines. 22, 23 are the upper edges of the upper pressure faces. These and points 16, 17 because of their maximum radial distances from the shaft axis, are the points of maximum imrnediate rotative pressure in their respective faces; and cross lines 24, 25

therefore indicate the alternative lines of maximum compressive force in the 'key from the imposed or power load, respectively from right hand and left hand shaft effort; and accordingly, in vice versa alternation, they represent the lines of maximum reduction of the residual compressive Stress in the key. 30, 31 (FIG. 4) are typical fiank faces of the plurality of serrations formed on the mutually contacting faces of the key halves A and B. 32 is the crest of a typical serration and 33 the fioor spacing apart two adjacent serrations. The crests and fioors must have respective clearance. 2-8 (FIGS. 2, 4) is the median plan of the key assemblage and of both keyways. 29 is the median and pitch plane of the set of serrations and it intersec'ts plane 28 at the mial-length of the key assemblage. 35, 36 are the mid-length crossplanes of A and B respectively, the Circled points 37, 38 indicating their respective nominal intersections with 28. The key as shown is in a set or expanded adjustment. Wheel -D, being axially adjustable in position, may serve to hold wheel E against movement to the right, as the parts are viewed in FIG. 1. Gap 39a indicates a small clearance provided for accommodation of any adjustment in the axial position of Wheels E and D for the lining up of gears, Chains, V-belts, etc. or for exact spacing of the two Wheels from the axially fixed bearing G. Depressions 34 (FIGS. 1, 2, 3, 6) are tool spots formed in the ends of the key halves. Turning now to FIG. 5. Ba is the B half of FIG. 4 key slightly modified in the upper face for the use of shim T at the lower face 6a. Shaft Ca is the same as C in FIG. 4 except that the keyway is cut deeper, as though by reason of either accident in original machining or re-machining in the course of maintenance. 28c is the median line of the shaft keyway as cut. Because of the overcut, the lip line 17a, relief surface 21a, gage point 15a and floor 27a are all lower (with reference to key elevation and arc of shaft) than their counterparts in FIG. 4. Hub Da is the same as hub D in PIG. 4 except that it median line ZSb is rotatecl slightly toward the left, radially about the shaft axis, from its FIG. 4 coincidence with the median lines of the key and shaft keyway. And the keyway wall of hub Da is largely broken away to more clearly show the key face alteration. 28a is the median line of the key itself, shifted slightly toward the left but remaining parallel with 28c. Broken line 3a is the original key face 3 of FIG. 4, now angularly altered to position 3b in order to match the angle of the keyway wall in its slight rotative displacement. This alteration illustrates the object of the relief area 4, namely to reduce the amount of metal to be removed and hence the labor required in such alteration. The alteration of face 3a to 3b will be understood as indicating also a corresponding alteration in face 1 (FIG. 4), except that there the greater thiekness of metal is removed at the lower edge of the face, tapen'ng to nothing at the upper edge. The face angle correction of FIG. and the altered relationship of the median lines of key and keyways as described above are typical of face angle correction generally and whether the upper or lower pair of faces are chosen for correction.

'In a modified construction (FIGS. 10, 11, 12) J' and K are the two halves of the key. Upper working faces 40, 4-1 and lower faces 44, 45 are interrupted by shallow median relief areas 42, 43 and 46, 47 respectively. These four reliefs are for the purpose of minimizing labor in any necessary fitting of the 'key because of mis-match of keyways, either in width or in angular position about the shaft axis. 48, 49 are the coplanar top areas of the halves. 59, 51 form a broad shallow relief in the top surface of the assemblage. 52, 53 are the bottom key areas similarly relieved in areas 54, 55. These two assemblage reliefs are for the protection of the crest and floor clearances of the upper and lower edges of the serrations from any deformation due to contact with the upper and lower keyway floors. The narrow reliefs 56, 57 are demarcations of upper and lower pressure faces and serve as tool clearances for possible exclusive filing or grinding alteration of one of the two faces. It will be understood that these three sets of reliefs are all and severally optional; may be used where appropriate in other key forms than that of FIGS. 10, ll and 12; and, all being formed in the die drawing of the key stock do not (in straight keys) involve additional or specific machining cost. 58 is the common arc of the shaft and bore and 59, 60 circled, the points of intersection of said are with the side faces. These points are at the lower edges of reliefs 56, 57 and coincide with the shaft keyway lip points. 61, 62 (PIG. 12) are the points of immediate maximum power pressure in the upper faces as the lip points 59, 60 are in the lower faces; and crossed lines 63, 64 correspond diagrammatically to cross lines 24, 25 in FIG. 4 in description and significance as to key forces. '65 (FIGS. 10, 12) is the median plane of key and both keyways and 66 is the median and pitch plane of the serrations; which latter are similar in form and function to those of FIGS. 1 to 5 and so need not be described again in detail. 67, 68 are the mid-length planes of the I and K halves respectively and circled points 69, 76 their intersections with the common pitch plane of serrations. The `key as shown is in a laterally contracted adjustment.

In the construction of FIGS. 7, 8 and 9, N and P are the two halves of the key and Q and R the two head posts for holding and extraction. The posts may be of standard taper pin form and tilted forward slightly as shown, for engagement advantage. The upper and lower side faces of the key may be conventional as shown or may have relief areas as in the key of FIGS. 10, ll, 12;

and in either case require no further particular description. The serrations are similar to those previously described. 72, 73 (FIG. 8) are respectively the median plane of the key and pitch plane of serrations. 78, 79 are the mid-length planes of the nominal engagement lengths of the key halves and circled 'points 80, 81 the intersections of these planes with common pitch plane 73. 74, are the sloping top engagement surfaces of the halves. 76, 77 are reliefs in the top surfaces and may be mach'ined with them. 82, 83 mark the ends of the nominal engagement lengths of the halves and the starting of the slopes. The key as shown is in a laterally contracted adjustment.

The present key, in each of the several described forms, consists of two supplementary members, in effect a pair of co-acting wedges with parallel outside faces, adapted for relatively guided longitudinal sliding engagernent` The relative alignment and relative Vertical positioning of the members are preserved by a series of longitudinal serrations of wedging interfit on the mutually contacting faces. The parallel outside faces of the members are the sides, the working faces, of the key. Relative length- Wise movement of the members, increasing or decreasing the width of the key as a whole, does not alter the height of it nor disturb the parallelism of the side faces. Such movement is used for the adjustment, setting or release, of the lateral face pressures. The key members are most conveniently matched in width at mid-length and the key therefore is at normal width or mean of total expansion range when the mid-points of the halves are opposite each other, as for example when, in FIG. 2, the lines 35 and 36 are aligned and the points 37 and 38 coincide. For this basic lengthwise wedging I prefer a slope of about one-eighth inch per foot` The serrations are preferably of truncated wedge form with fiat flanks having a pressure angle of about thirty degrees or included angle of sixty degrees. The fianks carry the entire contact load, the crests and fioors not touching. The fiank faces therefore have quite high normal pressure, the serration wedging `being compounded with the primary spreading force of the key. This high pressure is functionally important in two ways: -as prestress for the solid mutual footing of the key halves as against a certain Vertical shearing force at the joint; and for its frictional value as against casual relative length- Wise movement of the halves and consequent loss of adjustment in operation. And the mutual longitudinal friction of the key members should have a good margin of Safety over the friction of either half of the key with either the hub or the shaft, so that the setting will not be lost even though'one machine member, due to some extraordinary force, may be shifted 'axially with reference to the key. The shear force referred to above does not occur in the static and balanced pre-load condition of the key, but only from the load imposed in the transmission of power, alternatively along the lines 24 or 25 (FIG. 4) or 63 or 64 (FIG. 12). And although the Vertical shear force is not nearly as great as the main or horizontal shear load yet it is as sharp and as frequently alternating as the main shear; and the solid mutual footing of the halves is indispensable for maintenance of the keys external pressured contacts and so to its overall functionmg.

Now referring specifically to the key of FIG. l: This is the preferred form of the present invention because in it the pressures of the working faces are equalized or proportioned, exactly and automatically and (normally) without either fitting labor or selective assembly. The sides of the key are in effect a pair of oppositely and outwardly-directed blunt-angled wedges. They are here shown at a suitable included angle of degrees equally divided between upper and lower flanks. So in this split hexagon form all of the forces in and about the key, both residual and poWer-imposed, are carried upon a total of four wedgings: the primary spreading, the interfitting serrations and the two tactile engagements. For installation the halves are set together in their laterally contracted relation and the key placed in the sha-ft keyway. The hub member is then moved into position over the key. One or both of the key halves are then driven end- Wise by means of a tool engaging the head end of the appropriate half key. Tool spots, as 34 in FIGS. 1, 2, 3 facilitate this operation, especially if the key ends are inside the hub as here shown. In this setting-up a stationary half may be allowed to back against the farther end of the keyway as the other half is driven up. But preferably, if both ends of the key can be kept accessible for the setting, the one half is first advanced, as B from the left end (FIG. 2) through a substantial proportion of the adjustment range, and then the other half, as A, from the right end is driven into final setting, the B half being held meanwhile by a backup tool at the left end. There are two advantages in the twofend set-up, even though access at the one end may be constricted: the full maxirnum tightening range is obtainable; and the key may be released for disassembly by back-driving either half. In the tightening process (FIGS. 1-5 fonn only) the key first rises until the upper key flanks contact the walls of the hub keyway. Thereafter, as lateral expansion pressure is built up by the driving of either or both halves, the characteristic equalized (or proportional) pressuring of the four working faces occurs, combining and compensating, by Vertical adjustment of key assemblage position, for the net effect of all of the small dimensional Variations in the cross-section of the key 'and keyways.

Continuing the reference to the hexagonal key form: when, due to either accidental original overcutting of keyways beyond normal tolerance or the re-finishing of key or keyway faces in maintenance, a looseness occurs which is not compensable within the designed adjustment range, the fit may be easily and safely restored by introducing shims or interliners, integral or laminated, at one or more faces of the key. It is practicable and in certain circumstances may be advantageous to shim at any one, two or three faces, or at all four; but in general it is preferable to shim in two adjacent quadrants; either a horizontal pair of faces or a lateral pair, since such shimming strictly preserves the true face contacts of the key in both keyways and thus avoids all fitting labor except the thickness determination and placement of the shimming. A lateral two-face shim shifts the median line of the key toWard the opposite side of the keyspace but keeps it parallel with the common and trueradial medians of both keyways. However, as among the true-contact options, shirnming of the two lower faces is generally the most convenient for the assembler. And it facilitates cutting and placement to use continuous or one-piece shimming for the two faces. The reach of liner across the keyway floor does not interfere with floor clearance because the key is raised in the process, proportionately increasing the depth of the space. An occasion where one-face shim may be appropriate is where unusually close regulation of the longitudinal movement of the key halves is desired and shimming of the required thinness for two-face shimming is not at hand. In such case, the make-up being very light the angular disturbance of face contacts is also slight and may be neglected. The typical face correction of FIG. 5 and related explanation is based upon the use of a relatively heavy single-face shimming.

A distinctive utility in the shimming adjunct, beyond mere dimensional make-up in salvage and repair, is that it permits the keyage toraccommodate a certain range of positional mismat-ching of keyways, yet without loss of the Proportional pre-stressing Character. Such mismatching may be due to small inaccuracies in keyway location, in shaft or hub or both, in the use of two keys in one hub; or in the keying of two Wheels, as a pair of crank gears, ou one shaft, where exact axial alignment of Crank pins and/or gear teeth is required for true loading of teeth, connecting bars, shaft bearings, etc. In the latter case, discrepancy of keyway indexing in a twin crank gear assemblage, a critical consideration is that linear error at the key is multiplied at the crank pin -and gear teeth, usually by many times, because of the relatively great radius at the wheel periphery. There are two ways of applying the shimming to meet the resulting mis-match at one key space. One is by first reducing, sufficiently for key entry and normal free advance, one of the diagonally opposite key faces which are constricted in the mis-match key space and then, after determining and effecting the needed face angle corrections, supplyiing sufficient shimming at one of the un-constricted faces to secure simultaneous pressuring at all four faces. This method has the advantage that it confines all of the adaptive reduction to the key itself. The other way, which I prefer because it involves less hand labor in the fitting, is to overcut one keyway of the four involved, and preferably in a hub; place the key in the co-acting (shaft) keyway at the desired initial gripping adjustment; determine and make the angular correction in the 'two upper key faces so they Will be parallel to the overcut keyway faces, and then shim to firm contact, dividing the total make-up between left and right faces to suit the case. The angular corrections of the two key faces, by either method, are proportional to the angular displacement of the one keyway from its true common median relation to the co-acting keyway.

The broad normal function of keying is based upon free concentering of two keyways, with casual or only approximate index reference between shaft and wheel. For such cases as the preceding, where two keys or two or more keyed trains of power are to be synchronized, the shimmability of the compound wedge type of key, derived from wedge-backed incidence of the pressure faces, thus extends the utility of keys beyond the keying obje'ctive proper (that of angular holding of the members), to an old associated need, that of precise angular accommodation in machine assembly, for error in and the functional benefit of other machine parts than the key. This new feature of angular adjustability, although much less commonly needed than the old axial adjustment feature of keys in general, is classifiable as an actual extension of key utility. It tends to widen the key field in comparison with other full-torque hub fastenings, such as splining.

An optional feature shown in the keyage of FIGS. 1-5 is the shaft keyway lip relief or shouldering as first shown in the 'co-pending application referred to above, but which is equally appropriate for use with any form of the lateral expansion key of this application. The shoulder formation strengthens and provides clearance for the shaft keyway lip, preventing or minimizing the mutual impaction of shaft and hub keyway lips, which frequently is the main cause of shaft seizure.

Turning again to the key of FIGS. 10, 11, and 12, it represents an adaptation of the primary lateral expansion feature of the present invention to the external form of the commercially existing keyspaces of the standard square, straight (non-tapered) type of key. And t-he pressuring of lateral faces is obtained in useful degree; but the compartition of forces which is geometrically inherent in the rectangular form not only does not induce but actually prevents the balancing of upper against lower lateral forces and so deprives this hybrid construction of the four-face pressure equalization of the hexagonal form of FIGS. 1-5. In the dimensional terms and context of pre-Stress (the latter being of the essence of this immediate art) the hub and shaft keyway Widths of the commercial standard keyway are seldom if ever exactly equal in fact, even though nominally of the same width. Milling tolerances themselves represent one variable, and tolerable 'differences in smoothness of finish of the keyway Walls is another. These interfere seriously with simultaneous upper and lower lateral gripping. So

the equalization must be had or approximated by fitting; and for this purpose the shimrning which is permitted by the expansion feature may be useful. As to procedure, the key itself is used for gaging, separately and at equally firm set-up, the respective actual keyway widths. The linear difference in drive-up is noted and read, by a certain ratio, in terms of key width. (For example, assuming a slope of 1As-inc-h per foot in the serrated fa'ces, a drive-up difference of .192 inch, about z/m-inch, would indicate a difference of .002 inch in the width of the keyways.) A discrepancy may be met by widening the narrower keyway, by reducing one key entry to match the narrower keyway, by use of shimming in the Wider keyway, or by a combination of these accommodations. This equalizing of pressure should be done as accurately as possible; but if and when one face shimming is used, any necessary approximating should favor tightness of the shimmed fit for retention of the shim. Shim pieces should be cut long enough and so placed as to extend beyond both ends of the key and at least one end of the hub, this for convenience in placing, check of correct position after driving, for retention (by bending over ends of key or hub), and as tag to show the fact, location and thickness of shim in use. The fitting completed, the contracted key is then placed in the shaft keyway, With shim if any; the hub is moved into position and upper entry shim if any inserted, and the key then set up in the same manner as the FIG. 1 key. Of course, if the keyway has an open-end approach the wheel may be placed first and then the key slid into position and expanded.

The key of FIGS. 7, 8, 9 is an adaptation of the lateral wedging feature to a key suitable for interchange with another standard form, the "at (rectangular) tapered key, with provision for extraction corresponding to the extension with gib head of standard keys. (It will be understood that the top taper and the extension and 'extraction provision of this key may be applied as well' to the square form of FIGS. 10, 11, 12 and that the straight or non-tapered and headless form is equally applicable to the flat type.) In the FIG. 7 key the serrations are parallel With the lower face of the assemblage and, except for the partial cutting away of the top serration by the taper of the top face, are in all respects similar to those of the FIG. and FIG. l keys. As to procedure, the keyways are pre-gaged and pre-fitted separately and shirnming if required for simultaneous lateral grip provided, as with the FIG. 10 key. But this key requires a coordination of the top fitting with the side fitting. In the final setting of the key the tapered top surface 75 of the P half (FIG. 8) should be kept below and in rear of the surface 74 of the N half. The purpose is to insure that radial wedging shall not intefrfere With lateral wedging and to keep the two actions clearly distinguishable as to driving resistance. So the side seating should be sufi'iciently early in the adjustrnent range that line 79 will not pass line 78 in the final setting. Alternatively (if this restriction is inconvenient) the top surface 75 should be reduced in the fitting so that it will not bear against the fioor of the hub keyway. For intermediate locations of the hub member on the shaft an approach extension of the shaft keyway is required and used as in the standard integral driven key. The assemblage, in laterally contracted adjustment, enters the key space freely to within a short distance of gripping position. Shimming, if required, is then placed and the halves advanced together but with the N half leading and taking the radial wedging load, With the P half following closely enough to secure and maintain nearly solid lateral pressuring at the final advance of the N half. The final advance of the drive is in the P half, estahlishing the lateral set. The N half should not be driven extremely tight, for the radial pressuring is only auxiliary to the lateral in the functioning of the key; and the top surface friction must not be so great as to prevent the final side-seating movement. At this stage the further or excessive forward movement of the N half (due to the high frictional engagement of the serrated faces) may be prevented by a blockage or holding tool engaging the post Q. Release of the key is elfected by means of a suitable Wedging tool engaging pin R, as in the usual extraction of gib head standard keys. The post Q is spaced further back from the taper point 82 than post R is spaced from point 83. This prevents post Q from interfering with the wedging against post R. The P half tends to draw the N half with it but the latter may be then driven forward a little, elfecting the actual release of the lateral pressure.

The use of top taper and radial wedging here, in addition to the object of space adaptation, has a supplemental functional value both toward axial holding of the hub member and holding the key against lateral tilting. Both points are the more appropriate because the expanding rectangular key (flat or square) is deficient in some degree on both scores if not pre-fitted for good lateral grip in both upper and lower entries. And the benefit is reciprocal between the two grippings, for the assured solid lateral grip in at least one keyway, by preventing key tilting and the consequent rounding of the top and bottom surfaces tends to preserve the radial grip as against axial movement of the hub, a score in which the lateral gripping may be deficient because of weak frictional engagement in one keyway. The cooperation of the two functions, radial and lateral pressuring, at six faces can never be as complete or efi'icacious as in the actual merging of the forces at four faces as in the key of FIG. l; nor is it automatic, eXact or perfectly assured; but it tends toward the same objective.

I desire it to be understood that I may practice the invention with such variations of construction as may fall within the scope of the appended claims. Examples of such variations are: in the width-to-height proportions of key form; angles of convergence of key faces; exact form, proportions and/ or fiank angles of serrations; slope angle of serrated joint or of top face of a tapered key; and form or type of extraction or manipulation heads of key members.

I claim:

1. A machine key for holding machine elements against relative movement at mutually contacting surfaces, consisting only of two contacting and co-acting wedge members having complernentary Wedging angles, the contacting inner surfaces of said wedge members having a plurality of longitudinally extending and mutually interfitting serrations which prevent relative transverse movement of said wedge members, both of said wedge members being adapted for relative longitudinal movement, whereby the transverse width of the key assemblage may be increased or decreased; the outer surfaces of said wedge members being adapted to freely slide in the keyways provided in said machine elements until the key is tightened in said keyways by driving of either or both of said wedge members.

2. The invention defined in claim 1, wherein the key assemblage in cross section and as viewed in end elevation is generally hexagonal.

3. The invention defined in claim 1, wherein the key assemblage in cross section and as viewed in end elevation is generally rectangular.

4. The machine key as defined in claim 1 which further includes a relatively shallow medium relief area in each of a pair of said outer surfaces of said wedge members and extending throughout the length of said wedge members.

5. A machine key consisting only of two complementary co-acting wedge members having parallel outside working faces, said members being adapted for relatively guided longitudinal sliding engagement; said members each having a plurality of straight parallel serrations with fiat side walls extending longitudinally of the respective members, the side walls of the serrations being in 9 contact for Wedging interfit; the relative longitudinal movement of said members, when said serrations are interfitted, increasing or decreasing the over-all Width of the key as a whole, but without altering the height of the key or the parallelism of said Working faces.

6. The invention defined in claim 5, wherein the `serrations are all of truncated Wedge form with their side Walls having a pressure angle of about thirty degrees or an included angle of about sixty degrees; said side Walls carrying the entire contact load and the crests and fioors of the interfitted serrations being out of contact.

7. In combination, a cylindrical shaft member; a bored member mounted thereon; a keyway extending longitudinally in each of said members; a machine key in said keyways and engaging both members; the key consisting of two contacting and co-acting Wedge members having complementary wedging angles and each adapted for relative longitudinal movement and thereby for prestressing the keyWay side Walls; there being narrow relief areas formed upon said shaft and extending length- Wise of, outside of, and continguous to the shaft keyway; said relief areas lying within the cylinder of the shaft and having substantial clearance from the bore of said mounted member.

References Cited UNITED STATES PATENTS 408,835 8/1889 Grafton 287-5205 1,352,688 9/ 1920 Peterson 29-105 1,733,657 10/1929 Ericson 29-105 2,240,360 4/ 1941 Whitman 29-105 2,497,634 2/1950 Stevens 2.87-52.05 2,651,390 9/1953 Polanin 287-53 X 2,994,548 8/1961 McGogy 287-5205 3,121,2.89 2/ 1964 Eyolfson 287-103 FOREIGN PATENTS 598,445 6/ 1934 Germany.

CARL W. TOMLIN, Primary Examiner.

THOMAS F. CALLAGHAN, Examner.

T. A. LISLE, Assistant Examner. 

1. A MACHINE KEY FOR HOLDING MACHINE ELEMENTS AGAINST RELATIVE MOVEMENT AT MUTUALLY CONTACTING SURFACES, CONSISTING ONLY OF TWO CONTACTING AND CO-ACTING WEDGE MEMBERS HAVING COMPLEMENTARY WEDGING ANGLES, THE CONTRACTING INNER SURFACES OF SAID WEDGE MEMBERS HAVING A PLURALITY OF LONGITUDINALLY EXTENDING AND MUTUALLY INTERFITTING SERRATIONS WHICH PREVENT RELATIVE TRANSVERSE MOVEMENT OF SAID WEDGE MEMBERS, BOTH OF SAID WEDGE MEMBERS BEING ADAPTED FOR RELATIVE LONGITUDINAL 